Pneumatic tire

ABSTRACT

A pneumatic tire whose rim slip resistance and durability are improved by optimizing the shape of the bead base is provided. 
     A polygonal bead core  3  having a bottom  2  extending generally along the tire width direction is embedded in a bead portion  1 . The bead portion  1  has a bead base  6  extending between a bead heel  4  and a bead toe  5 . A maximum displacement point  11  is within a range of 25% or less of the width w of the bottom of the bead core with the third base point  10 . The interference t a  at the maximum displacement point  11  is 1.1 to 1.3 times as much as the interference t b  at the second base point  8 . the bead base  6  extends at least between the bead heel  4  and the first base point  8  and has a first tapered portion  12  with a taper angle θ 1  being identical with or greater by three degrees or less than a taper angle θ BS  of a bead seat of the standard rim R.

TECHNICAL FIELD

The present invention relates to a pneumatic tire and especially to aheavy-duty tire in which a polygonal bead core having a bottom extendinggenerally along the tire width direction is embedded in a bead portion,the bead portion having a bead base extending between a bead heel and abead toe. The present invention is aimed at improvements in rim slipresistance and durability.

RELATED ART

A pneumatic tire used as a heavy-duty tire for a truck, bus or the likeis mounted on a rim having a bead seat with a certain taper angle, sothat the tire has a configuration in which a bead core having apolygonal sectional shape is so embedded in a bead portion that itsbottom becomes generally parallel to the bead seat of the rim and inwhich the bead base is provided with a taper angle generally identicalwith the bead seat. However, a force which makes the bead core rotatingabout the bead core acts on the pneumatic tire having such a beadconfiguration due to the friction force between the bead portion and therim, and thus the bead toe is prone to be in a condition of being liftedup from the rim to decrease a contact pressure against the rim. As aresult, there has been a problem of inducing a displacement between thetire and rim (rim slip) by the time of steering, breaking or runningover convex/concave of the road surface.

In order to prevent such a rim slip, the bead portion is commonly shapedto have a larger interference which is defined as the amount ofcompression of the tire bead base in a radial direction of the tire whenmounted on a rim. With such a shape, the rubber element of the beadportion is compressed and elastically deformed to increase the contactpressure between the tire and rim when the tire is mounted on the rim.The rubber element is, however, deformed toward the radially outwarddirection since the bead heel is restricted its deformation in the widthdirection by the rim flange, whereas the metal element such as a wirechafer and a carcass is hardly deformed in both width and radialdirections since it is secured by the bead core. Thus, when theinterference of the overall bead base is uniformly increased, a largershearing strain occurs between the rubber and metal elements to incur aproblem that separations are easily caused in the bead heel.

In order to prevent the separation in the bead heel, the above-mentionedshearing strain has to be reduced. Thus, the conventional techniquereduces the shearing strain between the rubber and metal elements toinhibit the separation in the bead heel by enlarging the radius ofcurvature of the bead heel and thus reducing the amount of rubberlocated in the neighbor of the bead heel as well as by decreasing thecontact pressure between the widthwise outer portion of the bead baseand the rim seat, as shown in FIG. 5. Although such a tire may suppressthe separation in the bead heel at the early stage of use, a relativelylarge space S exists between the bead portion and the rim flange, sothat the rubber element of the bead portion is deteriorated and causes adeformation in filling the space S, which deformation is so-calledsettling, when the tire has been used for a long time. As a result, theshearing strain between the rubber and metal elements increases in thewidthwise outer direction, which also incurs a problem that separationsare easily caused.

In order to solve these problems, Japanese Patent Laid-Open No.2001-239812, for example, discloses a pneumatic tire in which the baseline is flexed to make the taper angle at the bead toe side larger thanthe taper angle at the bead heel side, as well as a concave portion isformed on the bead toe portion at the inner side along the bead portion.Japanese Patent Laid-Open No. 2001-150913 discloses a pneumatic tire inwhich the amount of compression is 1-5 mm at the point immediately belowthe center of the bead core and the maxim value of the amount ofcompression at the bead toe side in relation to the point immediatelybelow of the center of the bead core is 1.15-1.65 times as much as theamount of compression at the point immediately below the center of thebead core. The shape of the bead heel side of this tire is, however, notoptimized for effectively preventing the separation in the bead heel.

Japanese Patent Laid-Open No. 2001-213125 discloses a pneumatic tire inwhich the volume of the rubber chafer which is located at the bead heelside in relation to a radial line passing through the sectional centerof the bead core in the state where the tire is mounted on the rim andwhich is pushed away and deformed by the bead seat of the rim is 0.3-0.8times as much as the volume of the space which is located at the cornerwhere the bead seat of the rim continues to the rim flange and receivesthe rubber chafer pushed away and deformed by the rim mounting, therebyreducing the sharing deformation at the area corresponding to the beadheel and preventing the separation of the rubber chafer. The shape ofthe bead toe side of this tire is, however, not optimized foreffectively preventing the rim slip.

DISCLOSURE OF THE INVENTION

Accordingly, the object of the present invention is to provide apneumatic tire in which both of the rim slip resistance and thedurability are improved by optimizing the shape of the bead base.

In order to achieve the above-mentioned object, the present invention isa pneumatic tire in which a polygonal bead core having a bottomextending generally along the tire width direction is embedded in a beadportion, the bead portion having a bead base extending between a beadheel and a bead toe, characterized in that, in the widthwise section ofthe tire, when first, second and third base points are defined asintersections of lines extending radially inward from an outer endpoint, a widthwise center point and a inner end point, respectively, andthe bead base, and a maximum displacement point is defined as a pointwhere an interference is maximum, the maximum displacement point iswithin a range of 25% or less of the width of the bottom of the beadcore with the third base point as the center of the range, theinterference at the maximum displacement point is 1.1-1.3 times as muchas the interference at the second base point, the bead base extends atleast between the bead heel and the first base point and has a firsttapered portion with a taper angle being identical with or greater bythree degrees or less than a taper angle of a bead seat of a standardrim.

As used herein, the term “generally along the tire width direction”refer to a direction that extends within a range of 0-20 degrees, andpreferably 0-10 degrees in relative to the tire width direction. Theterm “interference” refers to the amount of compression of the tire beadbase in a radial direction of the tire when mounted on a rim. The terms“standard rim” refers to a standard rim (or a approved rim or arecommended rim) specified in an industrial specification, standard orthe like such as JATMA, TRA and ETRTO which are effective in the regionwhere the tire is manufactured, sold or used.

The bead base preferably has a second tapered portion extendingwidthwise outwardly from the maximum displacement point and having ataper angle larger than the taper angle of the bead seat of the standardrim by 10-14 degrees, and a third tapered portion extending widthwiseinwardly from the maximum displacement point and having a taper angleidentical to or smaller by five degrees or less than the taper angle ofthe bead seat of the standard rim.

The second tapered portion preferably continues to widthwise inside ofthe first tapered portion. In this case, it is more preferred that thefirst and second tapered portions contact with each other at the secondbase point.

The maximum displacement point is preferably located widthwise outsideof the third base point.

The interference at the first base point is preferably 0.7-1.0 times asmuch as the interference at the second base point.

It is preferable that the contact pressure between the bead portion andthe rim at the first base point is 0.6-0.8 times as much as that at thesecond base point and the contact pressure between the bead portion andthe rim at the third base point is 0.8-1.0 times as much as that at thesecond base point in the state where the tire is mounted on the standardrim.

The area defined by a line extending widthwise outwardly from the outerend point of the bottom of the bead core, a line extending radiallyinwardly from the outer end point of the bottom of the bead core, andthe outer profile line of the tire is preferably 0.93-0.97 times as muchas the area defined by the above-mentioned two lines and the outerprofile line of the rim.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a widthwise sectional view of a bead portion of arepresentative pneumatic tire according to the present invention;

FIG. 2 is a widthwise sectional view of the bead portion of the tire ofFIG. 1 showing in the state that the tire is mounted on a standard rimR;

FIG. 3 is an enlarged view of a neighborhood of the bead heel of thebead portion shown in FIG. 2;

FIG. 4 is a widthwise sectional view of a bead portion of a tireaccording to the prior art showing in a state that the tire is mountedon a standard rim R; and

FIG. 5 is a widthwise sectional view of a bead portion of ConventionalExample showing in a state that the tire is mounted on a standard rim R.

BEST MODE FOR CARRYING OUT THE INVENTION

In the next, explanation will be made on an embodiment of the presentinvention with reference to the accompanying drawings. FIG. 1 is awidthwise sectional view of a bead portion of a representative pneumatictire (hereinafter referred to as “tire”) according to the presentinvention, and FIG. 2 is a widthwise sectional view of the bead portionof the tire of in FIG. 1 showing in the state that the tire is mountedon a standard rim R.

In a bead portion 1, embedded is a polygonal bead core 3 having a bottom2 extending generally along the tire width direction. The bead portion 1also has a bead base 6 extending between a bead heel 4 and a beat toe 5.A carcass 7 is so disposed that it is turned around the bead core 3. Inthe bead portion 1, a first base point 8, a second base point 9 and athird base point 10 are defined as intersections of lines l₁, l₂ and l₃,respectively, extending radially inward from an outer end point C_(O), awidthwise center point C_(M) and an inner end point C_(I), respectively,and a maximum displacement point 11 is defined as a point on the beadbase 6 where an interference t is maximum.

And the major constitutional feature of the present invention is thatthe maximum displacement point 11 is located within a range of 25% orless of the width w of the bottom of the bead base with the third beadbase point 10 as the center of the range; the interference t_(a) at themaximum displacement point 11 is 1.1-1.3 times as much as theinterference t_(b) at the second base point 9; and the bead base 6extends at least between the bead heel 4 and the first base point 8 andhas a first tapered portion 12 with a taper angle θ₁ being identicalwith or greater than a taper angle θ_(BS) of a bead seat of a standardrim R by three degrees or less.

In the next, it will be discussed, along with its operation, how thepresent invention has adopted the above-mentioned construction.

As described in the above, it is popular for improving the rim slipresistance to form the bead portion in a shape that has a largerinterference. FIG. 4 shows the widthwise section of the bead portion 101in a state where such a tire is mounted on the rim R. The rubber elementof the bead portion 101 is pressed by the bead seat BS of the rim R tobe compressively deformed. In this regard, the rubber element of thebead portion 101 at the bead toe 105 side is a free end and thus ispushed aside to be largely deformed inwardly in the width direction, asshown by the arrow A. The rubber element located below the bead core 103is sandwiched by the bead core 103 and bead seat BS to increase thecontact pressure. The rubber element at the bead heel 104 side is afixed end supported by the rim flange RF of the rim R and thus cannot bepushed aside to be deformed in the width direction. Instead, it islargely deformed outwardly in the radial direction, as shown by thearrow B. The distribution of the contact pressure is shown in FIG. 4. Asillustrated, the rubber element of the bead portion 101 at the bead heel104 side is largely deformed outwardly in the radial direction, but themetal element neighboring the rubber element, the carcass 107 in FIG. 4is secured by the bead core 103 and, in addition, the metal elementhardly deforms itself. Therefore, the sharing strain between the rubberelement and the metal element increases and a separation is prone tooccur between the rubber element and the metal element.

In order to prevent the occurrence of such a separation, known is a tirein which the amount of the rubber element at the bead heel 104 side isreduced, as shown in FIG. 5. In such a tire, since the space S betweenthe bead portion 101 and the rim flange RF is relatively large, thesettling of the rubber element occurs and the rubber element is deformedto fill the space S when the tire has been used for a long time. As aresult, the shearing strain between the rubber and metal elementsincreases, which incur a problem that separations are easily caused.

It is known as the mechanism how the rim slip is caused that a forcemaking the bead core rotating about the bead core is firstly created dueto the friction force between the bead portion and the rim, and then thebead toe comes into being lifted up from the rim to reduce a contactpressure against the rim, thereby causing the rim slip. The inventor hasfurther studied the mechanism how the rim slip and the separation iscaused, and has found that the contact pressure around the third basepoint, and more specifically in the area of 25% or less of the width ofthe bottom of the bead core with the third base point as its centerlargely contributes to the rim slip while the contact pressure widthwiseoutside from the first base point largely contributes to the separation.The inventor, then, has reached an idea that the rim slip may beeffectively prevented without involving an increase of the sharingstrain at the bead heel side by making the interference larger toincrease the contact pressure while reducing the amount of the rubberelement at the bead heel side without occurring the settling to decreasethe contact pressure. However, if the space between the bead portion andthe rim flange is large as mentioned above, a separation may occur whenthe tire has been used for a long time. In view of this, the inventorhas conceived that if the bead base 6 is made in such a shape that themaximum displacement point 11 is located in the area of 25% or less ofthe width of the bottom 2 of the bead core with the third base point 10as the center of the area and the first tapered portion 12 extending atleast between the bead heel 4 and the first base point 8 has the taperangle θ₁ which is generally agreed with the taper angle of the bead seatof the standard rim as with an ordinal tire, the contact pressure aroundthe third base point 10 is increased, but the contact pressure widthwiseoutside from the first base point 8 is decreased and the space betweenthe bead portion and the rim flange becomes relatively smaller, as shownin FIG. 2, thereby improving both of the rim slip resistance and thedurability. The present invention has completed in this way.

In this connection, the interference t_(a) at the maximum displacementpoint 11 is configured to be 1.1-1.3 times as much as the interferencet_(b) at the second base point 9. This is because the contact pressureat the maximum displacement point 11 is insufficient and thus the rimslip cannot be effectively prevented when the interference t_(a) is lessthan 1.1 times of the interference t_(b), whereas the mountability ontothe rim is likely to be deteriorated when the interference t_(a) is morethan 1.3 times of the interference t_(b).

Further, the taper angle θ₁ of the first tapered portion 12 isconfigured to be agreed with or be larger by three degrees or less thanthe taper angle θ_(BS) of the bead seat of the standard rim. This isbecause an air leakage may unfavorably occur when the angle θ₁ issmaller than the taper angle θ_(BS) of the bead seat of the standardrim, meanwhile the space between the bead portion 1 and the rim flangeRF becomes excessively large to cause the settling of the rubber elementand thus the separation between the rubber element and the metal elementcannot be effectively prevented when the angle θ₁ is larger than thetaper angle θ_(BS) of the bead seat of the standard rim by more thanthree degrees.

The bead base 6 preferably has a second tapered portion 13 extendingwidthwise outwardly from the maximum displacement point 11 and having ataper angle θ₂ which is larger than the taper angle θ_(BS) of the beadseat of the standard rim by 10-14 degrees, and a third tapered portion14 extending widthwise inwardly from the maximum displacement point 11and having a taper angle θ₃ which is agreed with or smaller by fivedegrees or less than the taper angle θ_(BS) of the bead seat of thestandard rim. This is because, on the one hand, the second taperedportion 13 allows the distribution of the contact pressure in the areaof 25% or less of the width of the bottom of the bead core with thethird base point 10 as the center of the area, which largely contributesto the rim slip, to be relatively flat to further improve the rim slipresistance. On the other hand, this is because the mountability onto therim is likely to be deteriorated in the case of θ₃>θ_(BS), and an airleakage may be unfavorably caused in the case of θ₃<θ_(BS)−5°.

The second tapered portion 13 preferably continues to widthwise insideof the first tapered portion 12. This is because the contact pressure atwidthwise inside of the first tapered portion can be prevented fromdecreasing by extending the second tapered portion 13 continuously fromthe first tapered portion 12. In this case, it is more preferred thatthe first tapered portion 12 and the second tapered portion 13 contactwith each other at the second base point 9. This can prevent the contactpressure from locally increasing and thus the contact pressuredistribution of the first tapered portion 12 and the second taperedportion 13 becomes relatively flat to further improve the rim slipresistance.

The maximum displacement point 11 is preferably located outside of thethird base point 10. By locating the maximum displacement point 11 belowthe bottom 2 of the bead core, the maximum displacement point 11 issandwiched by the bottom of the bead core 2 and the rim, so that thecontact pressure may be more effectively increased.

Moreover, the interference t_(c) at the first base point 8 is preferably0.7-1.0 times as much as the interference t_(b) at the second base point9. This is because an air leakage may occur if the interference t_(b) isless than 0.7 times of the interference t_(b), while the contactpressure at the bead heel 4 side becomes excessive and the shearingstrain between the rubber element and the metal element is increased tocause a separation.

Furthermore, it is preferred that the contact pressure between the beadportion 1 and the rim R at the first base point 8 is 0.6-0.8 times asmuch as that at the second base point 9 and the contact pressure betweenthe bead portion 1 and the rim R at the third base point 10 is 0.8-1.0times as much as that at the second base point 9 in the state where thetire is mounted on the standard rim. This is because a relatively flatdistribution of the contact pressure which is effective for asuppression of the rim slip cannot be obtained when the contact pressureat the first base point 8 is less than 0.6 times of that at the secondbase point, while the contact pressure at the bead heel 4 side becomesexcessive and the shearing strain between the rubber element and themetal elements is increased to result in a separation when the contactpressure at the first base point 8 is more than 0.8 times of that at thesecond base point. In addition, the contact pressure at the third basepoint 10 is insufficient and thus the rim slip cannot be effectivelysuppressed when the contact pressure at the third base point 10 is lessthan 0.8 times of that at the second base point 9, while themountability onto the rim is likely to be deteriorated when the contactpressure at the third base point 10 is more than 1.0 times of that atthe second base point 9.

FIG. 3 is an enlarged view around the bead heel of the bead portionshown in FIG. 2. The area S₁ defined by a line l₄ extending widthwiseoutwardly from the outer end point C_(O) of the bottom 2 of the beadcore, a line l₁ extending radially inwardly from the outer end pointC_(O) of the bottom 2 of the bead core, and the outer profile line l_(T)of the tire is preferably 0.93-0.97 times as much as the area S₂ definedby the lines l₁ and l_(T) and the outer profile line l_(R) of the rim R.This is because a settling of the rubber element may occur and, as aresult, the shearing strain between the rubber element and the metalelement is increased to easily cause a separation when the ratio S₁/S₂is less than 0.93, while the mountability onto the rim is likely to bedeteriorated when the ratio is more than 0.97.

The descriptions above show only a part of the preferred embodiments ofthe present invention, and various modifications can be made within thescope of the appended claims. For example, the carcass may be covered bya reinforcing layer such as a wire chafer. In FIG. 1, shown is anexample in which each of the first, second and third tapered portionshas a linear sectional shape and these portions are connected like abroken line. Each of the first, second third tapered portions, however,may have a curved sectional shape and these portions may be connectedlike a curving line.

EXAMPLES

Next, a tire according to the present invention was experimentallymanufactured and its performances were evaluated, which is describedbelow.

A tire of Example is for a heavy load with the tire size of 55/80R63. Inthis tire, a hexagonal bead core with a bottom of 45 mm is embedded inthe bead portion. The maximum displacement point is agreed with thethird base point. The first tapered portion with a taper angle of eightdegrees extends between the bead heel and the second base point. Thesecond tapered portion with a taper angle of seventeen degrees extendsbetween the second base point and the third base point. The third basepoint with a taper angle of zero degree extends between the third basepoint and the bead toe. The tire also has the specifications shown inTable 1.

For comparison, a tire (Conventional Example) having the same tire sizeand bead core as those of Example, the specifications shown in Table 1and the bead base shaped as shown in FIG. 5 is also experimentallymanufactured.

Each of the above sample tires was mounted on the standard rim specifiedin TRA (size: 41.00×5.0, taper angle: 5°) to form a tire wheel, and thenand internal pressure of 600 kPa (relative pressure) was applied. Eachof the following tests was conducted on each of these tires.

1. Rim Slip Resistance

A sheet like pressure sensor was attached between the bead base of thetire of the above-mentioned tire wheel and the bead seat of the rim inthe state where no internal pressure was applied and the distribution ofthe generated contact pressure was measured. The compression force wascalculated from the summation of the measured values to evaluate the rimslip resistance. The evaluation results are shown in Table 1.

2. Durability

The above-mentioned tire wheels were made to run on a drum under thecondition of the tire load of 920-1500 kN and the running speed of 8km/h. After running 1,040 km, the length of the separation occurred atthe bead heel was measured and the durability was evaluated from themeasured value. The evaluation results are shown in Table 1.

The numerical values of the evaluation results in Table 1 are shown byindex ratio with the result of Conventional Example 1 as 100. The largerthe value is, the more excellent the performance is.

TABLE 1 Conventional Example Example First base point Interference (mm)7 6.5 Contact pressure (kN) 5500 5500 Second base point Interference(mm) 8.5 8.5 Contact pressure (kN) 5500 6800 Third base pointInterference (mm) 10 12.5 Contact pressure (kN) 3800 3800 Taper angle offirst tapered portion (°) 8 8 Taper angle of second tapered portion (°)— 17 Taper angle of third tapered portion (°) — 0 Void space ratio 0.780.95 Rim slip resistance 100 130 Durability 100 114

From the results shown in Table 1, it is appreciated that Example tirehas better anti-skid characteristics and durability as compared withConventional Example tire.

INDUSTRIAL APPLICABILITY

With the present invention, a pneumatic tire having improved rim slipresistance and durability of the tire can be provided by optimizing theshape of the bead base.

1. A pneumatic tire in which a polygonal bead core having a bottomextending generally along the tire width direction is embedded in a beadportion, the bead portion having a bead base extending between a beadheel and a bead toe, characterized in that, in the widthwise section ofthe tire, when first, second and third base points are defined asintersections of lines extending radially inward from an outer endpoint, a widthwise center point and a inner end point of the bottom ofthe bead core, respectively, and the bead base, and a maximumdisplacement point is defined as a point where an interference ismaximum, the maximum displacement point is within a range of 25% or lessof the width of the bottom of the bead core with the third base point asthe center of the range, the interference at the maximum displacementpoint is 1.1-1.3 times as much as the interference at the second basepoint, the bead base extends at least between the bead heel and thefirst base point and has a first tapered portion with a taper anglebeing identical with or greater by three degrees or less than a taperangle of a bead seat of a standard rim, wherein the bead base has asecond tapered portion extending widthwise outwardly from the maximumdisplacement point and having a taper angle larger than the taper angleof the bead seat of the standard rim by 10-14 degrees and a thirdtapered portion extending widthwise inwardly from the maximumdisplacement point and having a taper angle identical to or smaller byfive degrees or less than the taper angle of the bead seat of thestandard rim, wherein the first and second tapered portions contact witheach other at the second base point.
 2. The pneumatic tire according toclaim 1, wherein the second tapered portion continues to widthwiseinside of the first tapered portion.
 3. The pneumatic tire according toclaim 1, wherein the maximum displacement point is located widthwiseoutside of the third base point.
 4. The pneumatic tire according toclaim 1, wherein the interference at the first base point is 0.7-1.0times as much as the interference at the second base point.
 5. Thepneumatic tire according to claim 1, wherein the contact pressurebetween the bead portion and the rim at the first base point is 0.6-0.8times as much as that at the second base point and the contact pressurebetween the bead portion and the rim at the third base point is 0.8-1.0times as much as that at the second base point in the sat where the tireis mounted on the standard rim.
 6. The pneumatic tire according to claim1, wherein the area defined by a line extending widthwise outwardly fromthe outer end point of the bottom of the bead core, a line extendingradially inwardly from the outer end point of the bottom of the beadcore, and the outer profile line of the tire is 0.93-0.97 times as muchas the area defined by the above-mentioned two lines and the outerprofile line of the rim.
 7. A wheel assembly comprising: a standard rima pneumatic tire in which a polygonal bead core having a bottomextending generally along the tire width direction is embedded in a beadportion, the bead portion having a bead base extending between a beadheel and a bead toe, characterized in that, in the widthwise section ofthe tire, when first, second and third base points are defined asintersections of lines extending radially inward from an outer endpoint, a widthwise center point and a inner end point of the bottom ofthe bead core, respectively, and the bead base, and a maximumdisplacement point is defined as a point where an interference ismaximum, the maximum displacement point is within a range of 25% or lessof the width of the bottom of the bead core with the third base point asthe center of the range, the interference at the maximum displacementpoint is 1.1-1.3 times as much as the interference at the second basepoint, the bead base extends at least between the bead heel and thefirst base point and has a first tapered portion with a taper anglebeing identical with or greater by three degrees or less than a taperangle of a bead seat of the standard rim, wherein the bead base has asecond tapered portion extending widthwise outwardly from the maximumdisplacement point and having a taper angle larger than the taper angleof the bead seat of the standard rim by 10-14 degrees, and wherein thebead base has a third tapered portion extending widthwise inwardly fromthe maximum displacement point and having a taper angle identical to orsmaller by five degrees or less than the taper angle of the bead seat ofthe standard rim, wherein the first and second tapered portions contactwith each other at the second base point.
 8. The wheel assemblyaccording to claim 7, wherein the second tapered portion continues towidthwise inside of the first tapered portion.
 9. The wheel assemblyaccording to claim 7, wherein the maximum displacement point is locatedwidthwise outside of the third base point.
 10. The wheel assemblyaccording to claim 7, wherein the interference at the first base pointis 0.7-1.0 times as much as the interference at the second base point.11. The wheel assembly according to claim 7, wherein the contactpressure between the bead portion and the rim at the first base point is0.6-0.8 times as much as that at the second base point and the contactpressure between the bead portion and the rim at the third base point is0.8-1.0 times as much as that at the second base point in the sat wherethe tire is mounted on the standard rim.
 12. The wheel assemblyaccording to claim 7, wherein the area defined by a line extendingwidthwise outwardly from the outer end point of the bottom of the beadcore, a line extending radially inwardly from the outer end point of thebottom of the bead core, and the outer profile line of the tire is0.93-0.97 times as much as the area defined by the above-mentioned twolines and the outer profile line of the rim.